In recent years, an organic EL (Electro Luminescence) display device has been receiving attention as a thin, lightweight, fast response display device. The organic EL display device includes a plurality of pixel circuits arranged two-dimensionally. The pixel circuit of the organic EL display device includes an organic EL element and a drive transistor provided in series with the organic EL element. The drive transistor controls an amount of a current flowing through the organic EL element, and the organic EL element emits light at luminance in accordance with the amount of the flowing current.
The organic EL display device has a problem that luminance of a pixel drops with operating time. The reason why luminance of the pixel drops is that a light-emitting efficiency of the organic EL element decreases and characteristics of the drive transistor (e.g., threshold voltage) fluctuates with the operating time. As a method for solving this problem, there is known a method in which a current flowing inside the pixel circuit is read out from the pixel circuit via a data line and the like, and a video signal is corrected based on a result of measuring the read-out current (e.g., Patent Document 1).
Further, in relation to the present invention, Patent Document 2 describes a shift register in which pulse output circuits shown in FIG. 24 are connected in multi-stage. In FIG. 24, an output terminal O1 is connected to the pulse output circuit in the next stage, and an output terminal O2 is connected to a scanning line. A low level voltage VSS1 is applied to a power supply line connected to a transistor Q92, and a variable voltage VSS2 is applied to a power supply line connected to a transistor Q94. The variable voltage VSS2 is controlled to the low level voltage VSS1 in a normal mode, and is controlled to a high level voltage VDD or the low level voltage of VSS1 in an all-at-once mode. In the all-at-once mode, it is possible to output a scanning signal for display to a plurality of scanning lines collectively at the same timing.